There are two important components in the immigration spectrum. One is the illegal immigrants who cross the border and provide low-cost labor. The other end is the high level and technical part of the spectrum. The special skills labor market currently comes through the H1B visa system.
Both of these sources of immigration are important to business. Both of these seem to be anathema to unions. Unions are most effective in restraining the low-end immigration channels, but out of rote hostility to immigration they also oppose the high-end skills market.
Americans have always had a mixed and confused attitude toward immigration. We have done little to restrain immigration. On the other hand we have been very unhappy at times with the immigrants as they fill our labor demands. This is part of a 200 year old pattern. It is no different today. The complaints about border crossing are not relevant. The number of so-called illegals is only 3% of our total population. That is insignificant. Because this population is sending so much money back to Mexico and the other countries they come from the demand to emigrate from Mexico and these other countries is diminished.
The so-called Kennedy Immigration Reform of 1965 changed legal immigration from white Europeans to a global system. However this system is currently swamped with family repatriation.
The explosion of American commerce from the 1960s on is related to the rapid increase in free trade and imports, the dramatic expansion and improved quality of immigration as well as the end of our hereditary elite and the decline of unions. Since many of these things occurred at the same time it is hard to separate out just the importance of immigration.
However immigration is a very important function in the growth and vigor of American industry. Immigration is tied to globalized corporations who benefit from moving foreign employees back and forth inside the global entity. This labor mobility benefits significantly from a generous immigration policy.
Many people do not know that the business grad schools on the borders of the United States, in Mexico, are among the best business schools on the continent. We need those ambitious people who want to come to the United States.
I personally have worked in many countries as a consultant. Everyone benefitted and tens of thousands of jobs were created in other countries from my help. Tight immigration rules would have stopped me.